Influence of Hydrothermal Carbonization on Composition, Formation and Elimination of Biphenyls, Dioxins and Furans in Sewage Sludge

Abstract

In many areas of application, the influence of hydrothermal carbonization (HTC) on the composition of organic pollutants is still unexplored. In this study, sewage sludge (SS) was carbonized and the input as well as the hydrochar were examined for the organic pollutants: polychlorinated biphenyls (PCB), polychlorinated dibenzo-dioxins (PCDDs), and polychlorinated dibenzo-furans (PCDFs). The process temperatures of carbonization were 200 • C, 220 • C, and 240 • C and the holding time was 5 h for all tests. The total concentration of PCBs was relatively stable for all temperatures, whereas the toxicity equivalent (WHO-TEQ) at 200 • C and 220 • C increases compared to the input material. The strongest impact on toxicity was observed for PCDDs where concentrations were reduced for higher temperatures, whereas the toxicity increases by more than 16 times for temperatures of 240 • C. The concentrations and toxicity of PCDFs were reduced for all carbonization temperatures. In hydrochar from HTC at 240 • C, the limit values for the application of SS in German agriculture have been exceeded. The results indicate that the process conditions for HTC should be controlled also for SS with average contamination if the hydrochar is to be used as material, especially in agriculture.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

“…When considering the toxicity by TEQ, the total TEQ of PCBs and PCDD/Fs was raised 9 times with increasing temperature from 5.36 ng/kg in MS to 46.09 ng/kg in hydrochar obtained at 240 °C. This was mostly contributed by PCDDs, whose TEQ increased significantly from an initial 2.72 ng/kg to a final 44.5 ng/kg (Brookman et al, 2018). On one hand, it appears that HTC could dechlorinate POPs.…”

“…The diverse compositions of MS could lead to complex reaction pathways in HTP and the MS-derived hydrochar with abundant functionalities. Moreover, MS also contains valuable inorganic compounds, such as Na, K, Al, Ca, Fe, and Mg, along with pollutants and potential carcinogens, such as heavy metals, polychlorinated compounds, and PAHs, which tend to be recalcitrant to HTP and accumulated in hydrochar (Brookman et al, 2018;Chanaka Udayanga et al, 2018;Raheem et al, 2018).…”

“…MS-derived hydrochar showed the top level of I-TEQ (14.2 ng/kg) for PCDD/Fs among all tested biomass (all others below 6 ng/kg). Brookman et al (2018) investigated the effects of HTC (200-240 °C for 5 h) on PCBs and PCDD/Fs. Results presented that total PCDDs increased from 1.24 mg/kg in raw DS to 1.43 mg/kg in hydrochar obtained at 200 °C, but then suddenly decreased with increasing temperature to 0.12 mg/kg at 240 °C.…”

“…MS has been identified as a complementary P sink in regions with limited phosphate rock resources (Shi et al, 2019). However, MS, especially non-stabilized sludge, may also contain various hazardous materials, including pathogens (Lopes et al, 2020), organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) (Brookman et al, 2018), inorganic pollutants (e.g., heavy metals) , and emerging contaminants or micropollutants (e.g., antibiotics, hormones, pharmaceuticals, and personal care products) (Taboada-Santos et al, 2019).…”

Hydrothermal Carbonization as a Strategy for Sewage Sludge Management: Influence of Process Withdrawal Point on Hydrochar Properties

“…While multiple studies focused on nutrients recovery such as phosphorous [28][29][30] or probed the impact of processing conditions on the solid and energy yields of hydrochars produced from the HTC of sludge from one withdrawal point in the wastewater treatment (WWT) process [23,[31][32][33][34][35][36][37][38][39], the impact of upstream WWT processes on hydrochars is often not part of the experimental design. Thus, a primary goal of the present work was to determine the most viable point in the WWT process to employ HTC for sludge treatment from a solid fuel production and potential nutrient recovery standpoint.…”